If you find you are using an excessive amount of oxygen-scavenging chemicals, you may want to investigate the performance of your deaerater (DA) or feedwater heater. These pieces of equipment preheat the boiler feedwater and assist in the removal of non-condensible gasses such as oxygen and carbon dioxide which lead to feedwater, boiler and steam/condensate system corrosion.
- a deaerator is designed to operate with a temperature above 212 degrees F with a corresponding pressure that provides a temperature within 1 degree of the saturated steam. Typically deaerators provide feedwater with oxygen levels in the 5-7 ppb range when operating at specification.
- a feedwater heater is typically operated below 212 degrees F and is not as efficient at removing noncondensible gas as a DA is; however, they are useful at removing some of these undesirable gasses if operated at as high a temperature as possible.
Both of these systems require a vent for removal of the released gasses. A good rule of thumb is that a deaerator should have a continuous 18 inch plume of escaping steam above the deaerator vent line.
Monitoring a DA or feedwater heater's operating efficiency is easily accomplished using a spot check oxygen analysis kit. These colorimetric tests provide an instantaneous result of oxygen concentration on a sample of feedwater. The downfall is that this test result reflects just one point in time and may not represent efficiency at other times when conditions change.
What is a better means of measuring efficiency? Check tomorrow's blog for the answer.